add Key and Value type
refactored tag matching from database to writer

tag matching is independent of the database and can belong to the writer
package. also cleans up the database.Inserter interface.
add hstore_tags field type
add support for single table imports

- support type=geometry
- allow to load all tags
fix SelectRelationPolygons test
add columns as alias for fields mapping option
add support for 4326
disable ssl by default for PG connections to workaround renegotiation issues